Perhaps the most well known and widely used bodily tissue fixation systems typically employ metallic hardware, e.g., plates, screws, rods and the like, formed of biocompatible, corrosion resistant metals such as titanium and stainless steel. While such systems are generally effective for their intended purposes, they possess a number of inherent shortcomings. For example, for some surgical treatments it is not feasible to remove the hardware once it is implanted. As a result, the patient must permanently carry within his body substances foreign to his natural bodily tissue. In other situations wherein it is desirable or necessary to remove the hardware, a second surgical operation is required to perform such removal. Further, when using metallic fixation plates, to secure severed bone material, or the like, the inherent rigidity of the plates does not readily permit the plates to be adequately bent so as to closely conform to bone areas of small radii of curvature, such as cranial and facial bones, particularly those of children. As a consequence, optimum restraint of the bones against relative movement is not always achieved and the strength and/or appearance of the mended area, when healed, may not be entirely satisfactory.
In efforts to overcome some of the encumbrances of metallic bodily tissue fixation systems, an assortment of body absorbable bodily tissue fixation hardware and systems have been proposed, for example, in U.S. Pat. Nos. 4,905,680, 4,903,691, 4,539,981, 4,523,591, German Patentschrift DE 39 143 163, European Patent No. 0 260 222 and WIPO 90/07304.
U.S. Pat. Nos. 4,905,680 and 4,903,691 describe, in particular, bone fixation plates formed of body absorbable plastic material provided with a plurality of bores through which fasteners such as screws are inserted whereby the fasteners enter the bone to fasten the plate across a severed or fractured bone area in order to fixate the bone to promote stabilization during healing thereof. Although satisfactory for use in fixing severed bone areas of generally linear configuration (such as the elongated bones of the limbs) the bone plates taught in U.S. Pat. No. 4,905,680, by being relatively rigid similar to the previously discussed metallic plates, are not particularly well adapted to securing severed bone areas which may have small radii of curvature such as cranial and facial bones, especially those of a small child. That is to say, the plates cannot readily be brought into close conformance with highly curved bone areas whereby those areas may be effectively restrained against relative movement as is required to achieve rapid, sturdy and non-disfiguring mending of the bone.
German Patentschrift DE 39 143 163 discloses a bone fixation system comprising a body absorbable thermoplastic plate which is reinforced by carbon fibers and heated by an electromagnetic radiation heating means to cause the plate to soften and conform to the severed bone being repaired. Upon satisfactory conformance of the plate to the bone, the plate is then secured to the bone by suitable screws, or the like. While this system may serve to effectively restrain the bones being fixated from relative movement, two of the preferred means it may employ to heat the plate, i.e., either an infrared or a microwave radiation generator, if not cautiously operated, can cause irradiation of surrounding bodily tissue to a degree sufficient to overheat and thereby destroy the tissue. Moreover, the microwave or infrared generator heats the entire plate at once, which may not always be desired or necessary and which could render the plate too liquefied and structurally incoherent to be of any practical use, unless the surgeon exercises vigilant and continuous monitoring of the physical status of the plate during heating thereof. Also, the carbon fiber used for reinforcing the plate may not be fully biocompatible with and absorbable by the patient's body.
German Patentschrift DE 39 143 163 also teaches that the heating means may heat electrically conductive fibers in the plate by induction heating. Again, however, great care must be exercised so as not to heat the plate to a degree which would destroy its structural integrity and efficacy.
European Patent No. 0 260 222 teaches the concept of securing severed bone segments together by means of covering the severed area with flexible, body-absorbable plastic material and securing the material to the bone segments via body absorbable fasteners such as screws or rivet-like members. Aside from providing limited restraint against relative movement of the bone segments, the system taught therein requires bores of several millimeters to be provided in the bone to receive the fasteners. Such large diameter bores and fasteners may be acceptable for many bone repair situations but, due to their size, they limit the practical application of the system essentially to repair of relatively large bones. In fact, the screws are of such dimensions that they require a central longitudinal passage of sufficient size to internally receive along the full length thereof an elongated screwdriver shaft to drive the screw into the bone. The presence of the central longitudinal passage thus necessarily requires the screw to be of an unacceptably large diameter for small bone repair operations. The screw is further provided with a plurality of transverse flow passages in communication with the central passage so as to enable the necessary body fluid to enter the interior of the screw and effect decomposition of the screw not only from the exterior but the interior thereof as well. Hence, because of the physical dimensions of the screws, without the existence of the interconnected longitudinal and transverse passages, the time required for decomposition of the screws would be substantially increased, perhaps undesirably prolonging the bone healing process.
An advantage exists, therefore, for a body-absorbable bodily tissue fixation plate whereby the plate (such as a bone fixation plate) can be molded to closely conform to the shape of the bodily tissue being fixated. Such plate should be thermoplastic and readily bendable through the application of a series of spot heatings at predetermined sites thereon via appropriate heating apparatus without potentially sacrificing the physical integrity of the plate.
A number of apparatus for localized heating applications are known. One such device is the conventional hand-held, electrical resistance soldering iron commonly used to solder small-scale electrical or mechanical connections. The primary disadvantage of this sort of device, if it were somehow attempted to be utilized in a surgical operation of the type contemplated herein, is that its elongated heating element, which operates at high temperature along the entire length thereof, is quite likely to come into contact and burn the skin or other biological tissue of the patient and possibly the operator, particularly if the surgery is being performed in a rather deep surgical incision.
In this connection, U.S. Pat. Nos. 3,494,364 and 4,074,110 describe heating apparatus for, inter alia, cauterizing biological tissue in surgical operations. The heating apparatus disclosed in these references include heating wands having tips that are heated by electrical resistance in the case of U.S. Pat. No. 3,494,364 and conduction in the case of U.S. Pat. No. 4,074,110. In each of these patents, the wands include housings which do not lend themselves well to working in either deep incisions or small scale operations because their bulk precludes clear vision of the area being treated. U.S. Pat. No. 3,494,364 describes, for example, a heating wand housing having an outer diameter of approximately three-eighths of an inch, which, as will be appreciated later herein, is over three times the diameter of the heating wand of the present invention.
Moreover, the heating tips taught by these references saliently project from their respective wands and are substantially (as in U.S. Pat. No. 3,494,364) or entirely (as in U.S. Pat. No. 4,074,110) uninsulated. As a consequence, biological tissue in the vicinity of the treatment area is exposed to a material risk of being inadvertently damaged by the heating tips.
High frequency radiation heating apparatus may also be used for localized heating. However, if such apparatus are used to heat materials in close proximity to living tissue, the surrounding living tissue behaves like a dielectric heating material, i.e., the energy generated by the high frequency heating apparatus is diffused three-dimensionally throughout the surrounding body tissue at a rate and magnitude of heat transference which are related to the dielectric constants of the body tissue. Consequently, such methods and apparatus are quite difficult to control in terms of preventing tissue burn in delicate surgical operations.
Ultrasonic heating apparatus represent yet another potential means for localized heating. However, ultrasonic heating apparatus suffer from related disadvantages as those attendant to infrared or microwave radiation heating apparatus (discussed hereinabove in connection with German Patentschrift DE 39 143 163). That is to say, the thermoplastic plate and/or the biological tissue in the immediate vicinity of the treatment area, if the ultrasonic energy is not carefully controlled, may rapidly become exposed to an energy level sufficient to overheat and destroy the plate and, possibly, the immediately surrounding biological tissue.
Laser heating apparatus have achieved wide acceptance as surgical apparatus for cauterizing biological tissue. The heating energy produced by a specific laser is related to the type of element or compound whose atoms are stimulated to produce the laser beam. For example, a CO.sub.2 laser produces a beam in the infrared range having a wavelength of approximately 10.6 .mu.m, an Nd:YAG laser produces a beam also in the infrared range and has a wavelength of approximately 1.06 .mu.m, and an Argon laser produces a yellowish green to blue beam of approximately 0.455 .mu.m-0.515 .mu.m.
In surgical applications, laser energy is typically applied to the biological tissue being treated in short bursts rather than a continuous beam because the high intensity of most surgical laser beams is such that, if continuously applied, the laser light would eventually vaporize the area being treated.
The surgeon would have to invest a great deal of time and effort in becoming and remaining skilled in how to effectively apply the laser energy to the desired areas of the plastics contemplated to be employed by the present invention without overexposing the plastics or the surrounding bodily tissue to the intense laser energy. Further, laser equipment is somewhat unattractive from the perspectives of cost, maintenance and storage.
Surgical laser heating apparatus, even if hand-held are also rather cumbersome to use in that they normally require a complex system of mirrors and/or fiber optic cables contained in a bulky housing, thereby rendering it difficult to accurately direct the laser energy to the desired treatment area, particularly if the area being treated is deep within the patient's body. Additionally, surgical laser apparatus are expensive and they are normally rather difficult to sterilize.
Cauterizing forceps whose opposed tongs are connected to sources of electrical potential are also known. In the operation of these devices, a quantity of biological tissue is grasped by the tongs and high frequency electrical energy is conducted between the tongs through the biological tissue to selectively cauterize the tissue. As noted previously, however, control of the diffusion of the high frequency energy is difficult and tissue in the vicinity of the grasped tissue may become unintentionally cauterized by this procedure, especially if the forceps are inserted into a relatively deep surgical incision.
Additionally, cauterizing forceps are not effective in heating plastic because plastic is a poor conductor of electricity. A frequency generator in the gigahertz range would normally be required in order to produce the energy sufficient to heat absorbable plastic bone fixation plates of the types contemplated herein, but the expense such a generator would be prohibitive since the present cost of such equipment ranges from about thirty thousand to about fifty thousand U.S. dollars. Moreover, the frequencies produced by a gigahertz frequency generator could cause interference with other electrical equipment operating in the vicinity of the generator.
An advantage thus exists for a hand-held heating apparatus adapted for highly localized heating, particularly for surgical treatment applications, that is easily handled and sterilizable, that will not burn or otherwise damage biological tissue in the vicinity of the treatment area, and that can be accurately monitored and controlled.